Brake control apparatus



E. E. HEWITT 2 BRAKE CONTROL APPARATUS Filed Sept. 28, 1940 2 Sheets-Sheet l Oct. 14, 1941.

Vigil/A.

/sA P Oct 14, 194`1- E. E. HEwlTT 2,258,761

BRAKE CONTROL APPARATUS Filed Sept. 28, 1940 2 Sheets-Sheet 2 /MR.P

'OAR EQU/PMENT INVENToR ELLIS E.HE.W|T T ATTORNEY Patented Oct. 14, 1941 NETE D' ST.-

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Mem* j orrlcs BRAKE CONTROL APPARATUS Application. September 28, 1940, Serial No. 358,746'

Claims;

This. invention. relates to brake control ap-paratus, and more particularly to apparatus for controlling the brakes on railway vehicles in a manner to. prevent sliding. of the wheels due to application of the brakes thereon.

It is a matter of common knowledge to those skilled, in the art that if the brakes associated with railway vehicle wheels are applied to a degree exceeding that permitted by the adhesion between Wheels and, rails,. the wheels Will commence to slip and if the. brakes are not released promptly will reach a locked-wheel stage and thus slide. Sliding of the Wheels is objectionable not only because it damages the Wheels but also because. a sliding wheel is less effective than. a rolling wheel in producing retardation of the vehicle..

The term wheel slipping is generally understood to refer to a Wheel which is rolling at a spe'edless than that. corresponding tothe speed ofthe Vehicle, and the term Wheel sliding is generally understood to refer to a wheel which.

i'snot rollingr at all whilethe vehicle. is in motion. In describing the invention these accepted meanings of these terrnsare to be understood throughout.

When a wheel begins to slip', if the brakes thereon are promptly released wheel sliding may be avoided: and the slipping wheel' will return to the speed of non-slipping Wheels. An object of the present invention. is. to' provide novel means which will respond in the incipient. stage of Wheel' slipping to initiate a release. of the brakes causing' the wheels to slip so that said wheelsV may return to synchronous or non-slipping Wheel speed.

A cause ofv wheel. slipping may be bad rail conditions, in which case it is desirable that the force with which the brakes are applied'be lower than that employed under good rail conditions. For that reason it has been considered desirable that when the brakes are reapplied on a wheel Whichhas slipped,v the degree of reapplication ble made lower than the degree of the original application which produced' the slipping condition. Another object of the present invention is to. provide improved means. which will automatically operate .to limit the degree of reapplication oi the brakes, on a wheel which has once slipped'` during a givenbrake application period.

The theory has been advanced that if one or more Wheels in a train of vehicles should slip, such is' an indication that rail traction conditions may not be upto expectations and that consethroughout the train may be applied shouldv be made lower than under ordinary operating .conditions. In accordance with this notion it isa further object of the invention to provide means which will automatically operate to limit the range of degrees to which the brakes. throughout the train may be applied when one or more wheels on vehicle have slipped due to application of the brakes.

A yet further object of the invention is to provide a novel brake control apparatus for realizingv Detail' description y Referring rst to the locomotive or power car' brake equipment shown in Fig. `1, this equipment comprisesa brake valve device I, a main reservoir 2, a straightiair pipe 3 which it willrbe understood runs throughout the yentire length of the train, a main reservoir pipe 4*, which also extends` throughout the length of theptrain', a brakeA cylinder 5j, a relay valve device 6, a controlk mechanism T, and a wheel slipv detector devicey 8. Also provided in this equipment is a pressure operated' switch device 9..

Referring now to the brake equipment on the trailer cars, as shown in Fig. 1A, this equipment comprises an extension of the straight air pipe 3; an extension ofA the main reservoir pipe 4, a brake cylinder 5', a relay valve device. 6', a control mechanism 'l, and a Wheel slip detector device 8. The parts bearing the same reference characters as employed inV connection with Fig. 1, but with the prime added, are. to be understood as being duplicates of the correspondingY devices in Fig. 1. It will therefore be necessary to describe in detail only the aparatus. shown in Fig. 1. The brake valve device l is preferably of the conventional self-lapping type, that is, the type in which fluid under pressure is supplied from the main reservoir 2 to straight air pipe 3 at a pressure value corresponding to the degree or' extent of movement of handle IG into an application zone. It will be understood that when the handle I isV in released position. the straight air pipe 3` is connected to the atmosphere by way quently' the range of degrees to which the brakes 55 of an exhaust pipe l I trated, as many may be employed on each car as is found desirable.

'Ihe relay valve device 6 may be of conventional design, as for example as shown in Patent No. 2,096,491 granted to Ellis E..Hewitt on October 19, 1937. As will be understood from this patent, the relay valve device contains a piston I3 which is subject to fluid under pressure supplied to a chamber I4, and operates upon supply'of fluid under pressure to this chamber to in turn supply fiuid under pressure from the main reservoir pipe 4 to the brake cylinder 5 and brake cylinder supply pipe I5 to a degree dependent upon the degree of pressure established in chamber I4. It will be understood of course that when the pressure in chamber I4 is atmospheric pressure the relay assumes a position in which it vents the brake cylinder 5 and pipe I5 to the atmosphere.

In carrying out the purposes of the invention I have added to the relay valve device 6 a magnet valve device I6. This device is embodied in a casing having disposed therein a double beat valve I1, which is biased toward an upper seated position by a spring I8, and which is actuated to a lower seated position by an electromagnet therein when energized.

The control mechanism 1 is a mechanism comprised of several component parts, one component part including a diaphragm 20 subject on its lower side to pressure of fluid in a chamber 2I and on its upper side to atmospheric pressure present in a chamber 22 which is always open to the atmosphere by way ofV port 23. The diaphragm is connected by a stem 24 to one end of a lever 25. The other end of the lever 25 is connected to a stern 26 fastened to a diaphragm 21, which is subject on its lower side to pressure of iluid in a chamber 28 and on its upper side to pressure of fluid in a chamber 29 which is always open to the atmosphere by way of a port 36.

As will be observed from the drawings, the chamber 2I is connected to the straight air pipe 3 by branch pipe 3I. Further, the diaphragm 21 is arranged to engage the fluted stern of a supply valve 32, which valve is urged toward seated position by a spring 33.

'I'he control mechanism 1 further comprises a movable fulcrum for the lever 25 in the form of a roller 35. The roller 35 is rotatably secured to a carriage 36 which is slidable on a bar or projection 31 fastened to or integral with the casing of the mechanism 1. The carriage has its upper surface serrated or notched as may be seen at 38. A spring 39 has one end fastened to the carriage 36 and the other end fastened to the frame of the mechanism, so that the spring urges the carriage to a biased position to the right, as will be evident.

The right hand end of the lever 25 engages the uted stem of a release valve 40, which valve is urged toward a seated position by a spring 4I.

Disposed to the upper right of the control mechanism 1 is an adjusting device 42, which includes a cylinder having disposed therein a piston 43 biased to the right by a spring 44. The piston abuts against a slidable sleeve 45 which serves as a stem for the piston. The sleeve 45 is slidable in the supporting casing and is provided with an internal bore forming a cylinder in which a piston 46 is disposed. The piston 46 carries a stem one portion 41 of which is of larger diameter than the other portion 48. The smaller portion 48 slides in an aperture in the right hand end of the sleeve 45. The piston 46 is biased to the left of the bore in the sleeve 45 by spring 49. The sleeve 45 has rotatably secured thereto an adjusting pawl 50, which pawl is so shaped that its extreme end 5| may engage one of the serrations or notches 38 for the purpose of shifting the carriage 36 to the left.

The piston 43 is subject to the pressure of fluid established in a chamber 54, and the supply of fluid under pressure to and the release from this chamber is controlled by a magnet valve device 55. This magnet valve device comprises a double Valve arrangement 56 which is biased toward an upper or venting position by a spring 51, and is actuated to a lower or supply position by an electromagnet inside the casing of the device when energized.

For controlling the supply of fluid under pressure to act upon the piston 46, there is provided a furthermagnet valve device 60. This device also comprises a double Valve arrangement 6I which is urged toward an upper or venting position by a spring 62 and is actuated to a lower or supply position an electromagnet in the valve device casing when energized.

' For the purpose of locking the carriage in a position to which it has been moved, there is provided a mechanism comprising a cylinder 63 which contains therein a piston 64 urged to an upper position by a spring 65. The piston is actuated downwardly upon supply of fiuid under pressure to the pipe 3I to which it is connected. The piston 64 has connected thereto a stem 66 the lower end of which is pivotally connected to a locking pawl 61. This pawl has an end 68 thereof shaped to engage the serrations 38 on the carriage 36, and when so engaged serves to hold the carriage in its adjusted position.

As will be observed, the adjusting pawl 56 passes through an aperture 69 in the locking pawl 61, which aperture is formed to permit vertical movement of the locking pawl relative to the adjusting pawl. A spring 10 attached to the adjusting pawl reacts against the locking pawl to urge the adjusting pawl downwardly with respect thereto.

The pressure operated switch 9 is preferably of conventional design and, as shown, is connected to the straight air pipe 3. The function of this switch is to establish connection between contacts 12 when pressure to a low predetermined degree (as for example five or six pounds) has been established in the straight air pipe 3. This is for the purpose of connecting one terminal of a battery 13 to a train supply conductor 14. It will be observed that the other terminal of the battery 13 is connected to ground at 15.

The wheel slip detector device 8 may be of any convenient design, but I have illustrated the type of design disclosed and claimed in Patent No. 2,140,620, granted December 20, 1938, to Clyde C. Farmer. Briefly stated, this device is embodied in a casing having an inertia mechanism disposed on a shaft to which a pulley 16 is afxed. The pulley 16 .is preferably rotatably connected to some part of the vehicle which rotates at Wheel ages-,freie speed, as for example a` vehicle: axle. The device;

is iso/constructed-that whenthe speedof the axle or part towhich. it isiconnected diminishes. atA aY rate exceeding a chosenratethe devicewillfactuate to cause engagement of. contactl members IH. contacts 12' are connected togetherI the. battery 13 will be connected. to' two conductors 18? and; 19. This connection. will be maintained; so long-.1 as the axle or-rotating partxof the vehicle. con-- tinues'to reduce inspeed ata ratev abovea chosen rate. It willV thus be obvious that. the device 8y will` indicate when a wheel slips, and. during the slipping stage willv connect. conductors: 1lilv and 19; to the battery 13.

Further details of the. invention. willibe best understood from. the description of operation. of; the embodiment illustrated.

Normal brake application Assuming thatthe equipment has beencharged with-fluidiunder pressure in the customary manner, a brake application may be effected by. moving the handle Hlv of the brake valve IA into the application zone. This movement of the handleresults in rst closing the communication between the straight air pipe and the exhaust pipe II- and then in supplyingfluid:- underpressure tothe straightY air pipe from the main' reservoir 2 to a degree dependent upon the extent of move-- ment of the handle into the application Zone.

Fluid under pressure supplied to. the straight air pipe 3- will onthe locomotiveand each car the train flow by way of branch pipe 3|- to thechamber 2l and cylinder 6.3 in each. control mechanism 1, as well as toswitch device 9.- on. the locomotive. I

The pressure established in chamber 2|*` will act upon diaphragm 2Q and. cause it to move up wardly from the position shown in Fig.; l. This movement will rock lever 25- about the f-ulcrum roller 35 and thus actuate diaphragm 21 down-- wardly. Release valve 43,. which was formerly' held open due to engagement of the right end of, thelever 25 therewith, wil-14 be closedby'its spring. 4.1:-, and. supply valve 32 will be actuated to= un seated position. Fluid under pressurev will. thenow from the straightv air pipe 3 to the; relay pistonchamber It, by way of-v branch pipeS-I past; unseated supply valve 3.2, chamber 28,` pipev and. passage 8G, past now-unseatedvalve l1, and from thence to the relay piston chamber. As a result. of this the rela-y valve device- 6.- will operate toy supply fluid under pressure from the-main reservoir pipe 4 to the brake cylinder 5;

The flow to the brake cylinder above described, willy continue until the pressure acting incham-` ber 28 below diaphragm- 21v is sufficient toactuate. the diaphragm upwardly and permit spring 33- toseat supply valve 32, without at the same time unseating release valve 49. Flow tothe brakecylinder will then be terminatedbecause as ischaracteristic of the relay device 6- itr will repro-v duce in brake cylinder a pressure corresponding to that established inthe chamber I4.

The pressurein chamber 2-8- which will produce the lap action just described will bear a relationto the pressure established in chamber 2l, and in straight air pipe 3, as determined by the relation of the moment arm of lever tothe right of the fulcrum to the moment arm of the lever tothe left of, the fulcrum, and,l by the relation: between the areas of diaphragms 2i) and 21, as; Will be obvious, Itwill thus be seenr that during ay normal brake applicationY the; pressure estab..-

Asawill. be evident' from the drawings, if the'- lishedgin thebrake cylinder 5'. will. bear a definite.. relation; to the pressure established, in the: straight' air pipe 32' by the brake-valve device I.

During. the-.brake application, and; so long as ai.

v. low; pressure exists in the straight airy pipe 3;,

switch devicev 9 will maintain. contactsv 12 connected; and; piston. 64 in cylinder 63. will hold botlrlocking paw1'61 and adjusting pawl50 downwardly; inengagement with the notches 38. ThisI Y willinsure.-that carriage 3.6 will hold the fulcrum roller. 35i in'. the desired position.

Iniordery to release the brakes the brake valve'. handle lgisreturned torelease position, whereuponpressure in the straight air pipe 3 will. bereduced; to atmospheric pressure by flow to the atmosphere via exhaust pipe I l. The consequentl reductionv of'pressure in chamber 2| will result in. the-.pressure in chamber 28 moving diaphragm. 271-' upwardlyn far. enough to cause unseatingV of releasen valve @fr This will effect .consequent-f venting, ofthe'` relay chamber I4 which will further'result ina releasing pressure from the brake cylinder 5;

The brakes, of course can be graduated on oro1^ in'. accordance with. the operation justf described'.

Control during wheelv slipping Assuming now that the brakes have beenV ap.-V

- plied; in the-manner justdescribed, andi that. a

wheel or wheels to which the wheel slip detectorA 8 is connected begin to` slip,. the apparatus will? function as-follows: I

Ifthe slipping wheell orv wheels decelerat'e in speed,- above a` predetermined rate, the wheelislipl detector device 8 will; cause engagement., off the. contacts 1-1. This will result inconnecting-bat-j teryl 15a to. the two. conductors 1l!v and 19'.. Con-- d-uctcr 1-3- extends throughout the trainv and'will; cause magnet valve 5.5; in each control mecha'-` nism 1- to be energized. concurrently; the con-- nection of conductorY 1.9; to. the. battery will'. causer magnet-valve devices M5#v and 6i] on the-locomotive; or power caronly to be energized.

Energizationof the magnet valve device I6: om the power carwill result in actuation of' its.v double bea-t valve l1 to; lower' seated position. Chamber 24: willbethenclosed to supply of. fluid under pressure-from chamber 28 and will. be im media-tely vented to the atmosphere by way of? the open upper seat of the double beat valve andtheexhaust portv 82. This venting of the chamber- I-dtakes placei rapidly, and.' will result in rapid release of. iiuid under pressure from the brake cylinder 5.y 'Ihe purpose oi'. this is to release thee by wav of the now open lower seat oi double valve 55 andi branch pipe 84; Fluid under pres-.-

sure immediately flows to chamber 55'? and actua-tes piston. d3; to the left until it strikes the sleeve element 85. This movementv of the pistontothe lef-t carries with it thesleeve and con-- sequently the adjusting pawl New, as'breviously described, prior tothe move-- mentof'the piston djust. described, both the-ad-y Justingpawl 5t and the lockingv pawl 61 are; in enga-gement with the serrated.` edges 38g of' the carriage 36. Therefore when the sleeve 46 moves to the right it shifts the carriage 36 with it.

Alilnergization of the magnet valve device 60 results in the double valve 6I being shifted to lower seated position, whereupon the communir cation from the chamber to the left of piston'46 to the atmosphere by Way of exhaust port 86, which formerly existed, is closed and fluid under pressure is supplied from the main reservoir pipe and branch pipe 84 to this chamber by way of the flexible conduit 86. The right hand end of the portion 43 of the stem of piston 46 will be in engagement with the piston 43 so that the piston 46 cannot move to the right. However, the sleeve 45 is movable relative to the piston and under the action of iiuid pressure moves to the right until the right hand wall of the sleeve strikes the large stem portion 41. This results in shifting the carriage 36 further to the left. By virtue of the movement of carriage 36 just described the fulcrum roller 35 is positioned along the lever 25 to the left of its normal position, and is held there by the locking pawl 6'! so long as pressure above a low value is present in the straight air pipe 3.

It will be understood of course that since the magnet valve devices I 6 and 60 on the locomotive only are energized the carriage 36 in the control mechanism 1' on the cars is moved only half as far to the left as on the locomotive, it being observed that conductor 18 is the only one which extends throughout the train and is, under the conditions described, connected to the battery 13.

As soon as the slipping condition of the wheel has been arrested, and the wheel has returned to substantially synchronous speed, the wheel slip controller device 8 opens the contacts 11. The magnet valve devices 55 throughout the train, and the magnet valve devices I6 and 66 on the locomotive (or any car on which wheel slipping has taken place), will be deenergized. From the description thus far it will be apparent that the parts of the control mechanism 1 will return to the positions they occupied prior to the wheel slipping incident, with the exception of the carriage 36 which will be retained in its adjusted position by the locking pawl 61.

. With the magnet valve device I6 deenergized the relay device 6 will seek to establish in the brake cylinder a pressure corresponding to that in relay chamber I4. But assuming that no change has taken place in the pressure in straight air pipe 3 the pressure in relay chamber I4 will now be different. On the locomotive (where it was assumed wheel slipping occurred) the pressure in relay chamber I4 will be reduced to a lower value than existed before the wheel slipping incident occurred because the fulcrum 35 has now been shifted considerably to the left and, as will be obvious, a lower pressure in chambers I4 and 28 will be required to balance the initially established pressure in chamber 2 I.

On the cars (where it was assumed that wheel slipping did not occur) the pressure in relay chamber I4 will not be reduced as much as on the locomotive because the fulcrum 35 was not shifted as far to the left as on the locomotive.

From the foregoing it will be obvious that the equipment disclosed provides that on any vehicle on which wheel slipping takes place the apparatus on each car is conditioned to rst release the brakes (to cure the wheel slipping condition) and to then permit reapplication of the brakes at a lower value than existed before the wheel slipping incident. On the cars on which wheel slipping actually occurred the limit of reapplication is made lower than on other cars. Thus the liability of a recurrence of wheel slipping on the same car, or the occurrence of wheel slipping on other cars, will be greatly minimized.

I have illustrated and described my invention in connection with an air brake system, because that type of brake is at present a standard form of brake for railway vehicles, but it will be understood that the principle of the invention may be adapted to other forms of brakes. Therefore I do not wish to limit my invention to the details of the particular embodiment shown but embrace within its scope the various forms included within the spirit and terms of the appended claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a brake system for a train of vehicles, in combination, a pipe extending throughout the train and being arranged to have selected pressures established therein, control means on each vehicle in the train for eiecting an application of the brakes in accordance with the pressure established in said pipe, adjusting means associated with each control means for changing the relationship between the degree of application of the brakes and the pressure in said pipe, a wheel slip detector device associated with each vehicle for detecting slipping of vehicle wheels, and means relating said detector devices and said adjusting means whereby a single detector device on a vehicle having wheel slipping controls the adjusting means on that vehicle in one manner and controls the adjusting means on vehicles having no slipping wheels in a different manner.

2. In a train brake system for a train of vehicles, in combination, brake applying means on each vehicle, a train pipe to which fluid under pressure is supplied to selected degrees, means responsive to the degree of pressure established in said pipe for causing said brake applying means to apply the brakes to a proportionate degree, a rst adjusting means for adjusting the relationship between the degree of brake application and the degree of pressure in said pipe, a second adjusting means for further adjusting the relationship between the degree of brake application and the degree of pressure in said pipe, a wheel slip detector device on each vehicle, and means relating said wheel slip detector devices to said rst and second adjusting means in a manner such that a wheel slip detector device operating in response to wheel slipping on a given vehicle operates both the iirst and second adjusting means on that vehicle, and operates only the said rst adjusting means on all other vehicles in the train.

3. In a brake system for a train of vehicles, in combination, a train pipe in which pressure is established to a chosen degree to effect an application of the brakes, a mechanism on each vehicle for applying the brakes to a degree proportional to the chosen pressure in said pipe, an adjusting mechanism for changing the re1ationship between the degree of brake application and the degree of pressure in said pipe, means responsive to slipping of a vehicle Wheel on one vehicle for actuating the adjusting means on that vehicle to vary the relation between the degree of brake application and the pressure in said pipe in one ratio, and operative to actuate the adjusting means on all other vehicles to vary the relation between the degree of brake application and the pressure in said pipe in a different ratio.

4. In a vehicle brake system, in combination, a brake cylinder, a pipe in which pressure is established to effect an application of the brakes, means including a positionable element for establishing in the brake cylinder a pressure bearing a relation to the pressure in said pipe according to the position of said element, a rst adjusting means operative to move said element to one degree, a second adjusting means operatve to move said element to a further degree, and a wheel slip detector device for controlling said two adjusting means.

5. In a vehicle brake system, in combination, a pipe in which pressure to a chosen degree is establishable to initiate an application of the brakes, means for eiecting an application of the brakes to a degree proportional to the degree of pressure established in said pipe, means including an element movable to diierent positions to vary the proportionality between the degree of application of the brakes and the degree of pressure in said pipe, electro-responsive means for shifting said element to a plurality of positions, and locking means responsive to the pressure in said pipe for locking said element in any one of said positions.

6. In a vehicle brake system, in combination, a pipe in which pressure is established to initiate an application of the brakes, a brake cylinder, means for establishing in said brake cylinder a pressure proportional to that established in said pipe, means including an element movable from a biased position to a plurality of other positions for varying the ratio between brake cylinder pressure and that established in said pipe, a wheel slip detector device, means controlled by Wheel slip detector device for controlling movement of said element to said plurality of positions, and locking means responsive to the pressure in said pipe for locking said element in any position to which it is moved.

'7. In a brake system for a train of vehicles, in combination, a train pipe to which fluid under pressure is supplied to a chosen degree to initiate an application of the brakes, brake applying means on each vehicle, means on each vehicle for causing said brake applying means to produce an application o the brakes to a degree proportional to the degree of pressure established in said pipe, a train electrical conductor, a local electrical conductor on each vehicle, means responsive to energization of said train conductor for changing the ratio between the degree of application of the brakes throughout the train and the pressure in said pipe, means on each vehicle responsive to energization of the local conductor on that vehicle for further changing the ratio between the degree of the application of the brakes on that vehicle and the pressure in said pipe, and a wheel slip detector device on each vehicle operable upon slipping of a wheel on that vehicle to energize both said train conductor and the local conductor on that vehicle.

8. In a brake system for a train of vehicles, in combination, a train pipe to which fluid under pressure is supplied to initiate an appllcation of the brakes throughout the train, at least one brake cylinder on each Vehicle for applying the brakes, a control mechanism on each vehicle for establishing in each brake cylinder a pressure proportional to the pressure established in said train pipe, said control means including an element movable to diierent positions to change the ratio between brake cylinder pressure and the pressure in said train pipe, a wheel slip detector device on each vehicle in the train, means on each vehicle operated in response to a wheel slip operation of the wheel slip detector device on that vehicle for promptly releasing fluid under pressure from the brake cylinder on that vehicle, and for resupplying uid under pressure to the brake cylinder upon cessation of wheel slipping on that vehicle, means responsive to the same operation of said wheel slip detector device for positioning said element on said vehicle to change the ratio between brake cylinder pressure on the said one vehicle and that in said train pipe to one degree, and means on each vehicle responsive to the same operation of said one wheel slip detector device for changing the ratio between brake cylinder pressure on all other vehicles and the pressure in said pipe to a different degree.

9. In a vehicle brake system, in combination, a brake cylinder, a pipe to which iluid under pressure is supplied to initiate an application of the brakes, means including a beam having a movable fulcrum for establishing in the brake cylinder a pressure bearing a relation to the pressure in said pipe according to the position of said fulcrum, means for effecting a release of the brakes upon slipping of a vehicle wheel due to application of the brakes, and for reapplying the brakes when the wheel slipping condition has substantially ceased, and means operable automatically in response to the wheel slipping condition for positioning said movable fulcrum so that the pressure reestablished in the brake cylinder following wheel slipping bears a different ratio to the pressure in said pipe than did the initial brake cylinder pressure which produced the wheel slipping condition.

10. In a brake system for a train of vehicles, in combination, a straight air pipe arranged to extend throughout the train' and to have fluid yunder pressure supplied thereto to initiate an application of the brakes, at least one brake cylinder on each vehicle in the train, means on each vehicle for establishing in each brake cylinder a pressure proportional to the pressure established in said pipe, an electrically operated valve means on each vehicle for eiiecting a release of fluid under pressure from the brake cylinder independently of variation of pressure in said pipe, and for also eiecting a resupply of iiuid under pressure to said brake cylinder, adjusting means on each vehicle for varying the ratio between brake cylinder pressure and the pressure in said pipe, and a device on each vehicle responsive to slipping of a vehicle wheel or wheels due to application of the brakes for controlling the electrically operated valve device on the same vehicle and the adjusting means on all Vehicles, 

